1. Field of the Invention
The invention relates to a metering pump, particularly for metering liquid components of reaction resin compounds, including a reciprocating displacement member, an intake valve designed as a dish valve and a discharge valve designed as a dish valve.
2. Description of the Prior Art
Reaction resin compounds are produced by mixing precisely prescribed quantities of resin and hardener, whereby a plurality of resins and a plurality of hardeners are employed in many cases. Moreover, additional substances such as fillers, dyestuffs, adhesion promoters, accelerators and the like can also be distributed to the resin and the hardener components. Modern preparation systems for such reaction resin compounds are composed of at least two supply reservoirs for the liquid components or pre-mixtures, metering devices following downstream of the supply reservoirs, and a mixing unit, whereby a static or dynamic flow-through mixer or larger mixing vessels are employed as the mixing unit. Oscillating displacement pumps such as, for example, piston pumps, diaphragm pumps or bellows pumps are, in particular, utilized as metering devices for components containing fillers, whereby rotating displacement pumps such as, for example, gear pumps can be utilized as well for unfilled components. Given the metering pumps having reciprocating displacement members which are employed particularly for metering components containing fillers, both an intake valve as well as a discharge valve are required per displacement member. Automatic valves such as, for example, spring-loaded ball valves, poppet valves or conical valves are thereby usually employed, these, however, being actuated only due to the differences in pressure in the pumping medium generated by the movement of the displacement member (German OS No. 28 51 188). This means, for example, that conveying from a supply reservoir containing a partial or full vacuum can only be reliably carried by means of elevating the hydrostatic pressure or by increasing the pressure elevation in the pumping medium by means of a preliminary pump. Frequently, however, it is necessary to meter the components from a vacuum. For example, when casting electrical high-voltage component parts, the components of an epoxide casting resin compound must be metered from a vacuum of, for example, 0.5 through 100 mbar. Moreover, metering pumps having automatic, spring-loaded valves involve the risk that granular or fibrous impurities will be retained between the valve seat and the movable valve part. This, however, leads to a temporary or permanent malfunctioning of the metering pump since the corresponding valve is held open by the seized impurity and is only partially pumped or not pumped at all.
Metering pumps designed as piston pumps are already known wherein a common intake and discharge valve fashioned as a rotary slide valve is situated in the pump head. Depending upon the position of this rotary slide valve controllable in constrained fashion from the outside, the work chamber in the pump head is then connected either to a supply reservoir or to a discharge pipe (Lueger Lixikon der Technik, Volume 8, 1967, Deutsch Verlags-Anstalt, Stuttgart, pp. 2 and 3). A very precise metering is enabled by such a rotary slide valve, since no changes in the volume in the hydraulic system ensue during the opening and closing events. On the other hand, the rotary slide valve is subject to extremely high wear, particularly when liquid components of reaction resin compounds which contain abrasive fillers are to be metered. Leakiness then arises as a consequence of this wear, a metering of components from a vacuum being impossible from the very outset due to the leakiness.